Art of making leatherboard



Patented Sept. 14, 1937 UNITED STATES PATENT OFFICE ART OF MAKING LEATHERBOABD N 0 Drawing.

6 Claims.

This invention relates to a method of making leatherboard which is also known as heeling board. These two terms are used interchangeably by persons skilled in the art to denote a material made from a furnish composed principally of leather scrap-by board-making processes which involve disintegration in a beating engine, and subsequent formation into sheets or slabs on a wet machine. The product usually contains some paper (generally not over 15%), introduced for process purposes and to impart certain desirable characteristics to the material, together with more or less leatherboard scrap. In this specification the term "leatherboard" will be used to denote such a product without regard to the proportions of constituents, provided there is present suificient leather to give it the desirable properties usually ascribed to the presence of leather fiber.

Leatherboard manufactured by the usual process is of a rather dark, unattractive color, undoubtedly due to the presence of iron-tannate inks formed in the leatherboard during its fabrication by chemical reaction between the tannins present in the leather scrap and the iron of the fabricating apparatus.

The most extensive commercial use of leatherboard is in the manufacture of heels for boots and shoes. Shoe heels made from the common dark colored leatherboard do not match the color of either the uppers or the soles made of hide leather, and this fact has resulted in the use of leather for the manufacture of heels in many cases where leatherboard would have been used but for its dark color.

In my United States Patent No. 1,975,556, I disclosed a process for treating leatherboard by subjecting it to the bleaching action of certain chemicals, the preferred embodiment of which was oxalic acid, to thereby remove the dark color of the iron-tannate inks either throughout the entire cross section thereof or in the outer crosssectional zones. I have now discovered that by the use of a solution containing an arsenic acid, such as orthoarsenic, pyroarsenic or meta-arsenic acid, the dark color of the iron-tannate inks may be removed to provide a leatherboard product having substantially the natural color of the leather fiber wherever it has been treated with said acid.

The primary object of this invention is to provide an improved method of manufacturing leatherboard which has the natural color of leather fiber.

Another object is to provide an improved Application April 6, 1936, Serial No. 73,019

method of manufacturing leatherboard which has the natural color of leather fiber in any desired cross-sectional zone or zones.

The arsenic acid solution may be applied to the furnish or to the leatherboard product in any of 5 the following ways:in the beater, in the vat, by dipping the leatherboard in the form of sheets or slabs in a solution of the acid, by spraying a solution of the acid upon one or both surfaces of sheets or slabs of the leatherboard, or by spraying m a solution of the acid upon one or more layers of the leatherboard as it is being built up on the wet machine. It will be apparent that suitable ventilation or other means should be provided to eliminate the health hazard incident to the use of arsenic compounds.

As illustrative of the application by dipping, a sheet of leatherboard is dipped in an aqueous solution of orthoarsenic acid of between 1% and 10% concentration. A 5% concentration gives a pale colored product of substantially the natural color of the outer cross-sectional areas of a cut section of hide leather Less concentrated solutions do not produce a leatherboard of such pale color. 25

The required dipping time depends upon the thickness and density of the leatherboard and also upon the flnal cross-sectional color effect which is desired. In making a product in which the dark color of the iron-tannate inks is removed from its entire cross-section it is necessary tokeep the board immersed in the solution long enough to permit the solution to penetrate the entire thickness of the board and thus allow it to come in contact with the iron-tannate inks throughout its entire thickness. In the case of boards of average thickness and density, adipping time of five minutes or more is sufficient. In producing a product which has pale colored outer cross-sectional zones and a dark colored center cross-sectional zone or core, the leatherboard is dipped in the solution only a sufiicient time to allow penetration into the outer cross-sectional zones, usually between thirty seconds and five minutes for boards of average thickness and density. The center cross-sectional zone into which the solution does not penetrate thus retains its original dark color, and in the outer cross-sectional zones the dark color is removed by the acid solution.

A test run may be made with a sample taken from the leatherboard to be treated, to determine the proper dipping time to produce the desired cross-sectional color effect.

By means of suitable concentrations and suit- 55 able dipping times in the use of the other arsenic acids, I have found it possible to produce results substantially similar to those produced with orthoarsenicacid. Reference to the literature leads me to believe. however, that pyroarsenic and meta-arsenic'acids when embodied in a water. solution do not maintain their identity but form orthoarsenic acid.

So far as I have been able to determine from a search of the literature I am the first to use arsenic acids to eliminate or remove the dark color due to the iron-tannate inks and to thereby liberate the natural color ofthe leather fiber. In use of these acids for the manufacture of a product having light colored cuter cross-sectional zones and a dark colored core or center cross-sectional zone, the lines of demarcation between the dark zone and the light zones are not as sharp as the corresponding lines in the product produced with oxalic acid, the preferred embodiment of my prior patent, and. for this reason the resultant product of my present invention provides a more softly blended color effect which is deemed highly desirable in certain uses of 26 the product.

It is to be understood that the foregoing disclosure is merely illustrative of my invention and is not to unduly restrict the scope of the following claims. It is also to be understood that my invention is not dependent upon any explanations or theories which I have set forth as descriptive of the actions involved, nor dependent upon the soundness or accuracy of any theoretical statements so advanced.

I claim:

1. The method of making leatherboard which comprises subjecting ieatherboard containing iron-tannate inks to the action of a solution containing an arsenic acid.

2. The method as defined in claim 1, wherein the arsenic acid solution has a concentration of from 1% to 10%.

3. The method as defined in claim 1, wherein the arsenic acid solution has a concentration of about 5%.

4. The method as defined in claim 1, wherein the arsenic acid is o'rthoarsenic acid.

5. The method as defined in claim 1, wherein the arsenic acid is pyroarsenic acid.

6. The method as defined in claim 1, wherein the arsenic acid is meta-arsenic acid.

HER W. RICHTER. 

